A 2.4-GHz MEMS-Based Oscillator with Phase Noise of -138 dBc/Hz at 100 kHz Offset and 226 dBc/Hz FoM

A 2.4-GHz MEMS-based oscillator is presented with gm-boosting technique. A novel Darlington cell with a dynamic self-body-biasing scheme is proposed to boost the transconductance and to shorten the start-up time without introducing additional parasitics to the resonant tank. A 2.4-GHz MEMS resonator is used for high Q resonant tank. The proposed oscillator core is fabricated in a 180-nm CMOS technology. Measurement result shows that the oscillator achieves a phase noise of -138.23 dBc/Hz at 100 kHz offset and a figure-of-merit (FoM) of 226 dBc/Hz. The DC power consumption is 0.98-mW from a 0.7-V supply voltage. The total chip area is 0.65 × 0.57 mm² including the pads.

I. Introduction

As an essential module, RF oscillators have received extensive attention and research from both academia and industry. Micro-Electro-Mechanical-System (MEMS) oscillators are attractive alternatives to quartz owing to their high Q-factor (>1000), small size, integration potential and low cost. The high Q characteristic of crystal and MEMS resonator is beneficial to improve the phase noise performance. However, it results in a longer start-up time inevitably, the typical start-up time of crystal is relatively long (~ms) [1]. Shortening the start-up time of the oscillator plays a positive role in saving power consumption and reducing bit error rate, especially for heavily duty-cycled systems [2].